Quarterly report pursuant to Section 13 or 15(d)

Fair Value (Details)

v3.19.1
Fair Value (Details) - USD ($)
$ in Thousands
Mar. 31, 2019
Dec. 31, 2018
Fair Value    
Investments at fair value $ 116,293 $ 116,805
Estimate Of Fair Value Fair Value Disclosure    
Fair Value    
Investments at fair value 126,627 125,911
U.S. treasury bills    
Fair Value    
Investments at fair value 2,293  
Government-sponsored enterprises securities    
Fair Value    
Investments at fair value 2,486 7,872
Corporate bonds and commercial paper    
Fair Value    
Investments at fair value 111,514 108,933
Fair value inputs Level 1    
Fair Value    
Investments at fair value 10,334 9,106
Fair value inputs Level 2    
Fair Value    
Investments at fair value 116,293 116,805
Fair value measurements recurring | Money market funds | Estimate Of Fair Value Fair Value Disclosure    
Fair Value    
Investments at fair value 10,334 9,106
Fair value measurements recurring | U.S. treasury bills | Estimate Of Fair Value Fair Value Disclosure    
Fair Value    
Investments at fair value 2,293  
Fair value measurements recurring | Government-sponsored enterprises securities | Estimate Of Fair Value Fair Value Disclosure    
Fair Value    
Investments at fair value 2,486 7,872
Fair value measurements recurring | Corporate bonds and commercial paper | Estimate Of Fair Value Fair Value Disclosure    
Fair Value    
Investments at fair value 111,514 108,933
Fair value measurements recurring | Fair value inputs Level 1 | Money market funds    
Fair Value    
Investments at fair value 10,334 9,106
Fair value measurements recurring | Fair value inputs Level 2 | U.S. treasury bills    
Fair Value    
Investments at fair value 2,293  
Fair value measurements recurring | Fair value inputs Level 2 | Government-sponsored enterprises securities    
Fair Value    
Investments at fair value 2,486 7,872
Fair value measurements recurring | Fair value inputs Level 2 | Corporate bonds and commercial paper    
Fair Value    
Investments at fair value $ 111,514 $ 108,933